The invention relates to an operating circuit for a load. Discharge lamps, chiefly compact fluorescent lamps, come into consideration as the load.
Use is made in discharge lamps of operating circuits and electronic ballasts which can, for example, have a half-bridge oscillator with mains supply via a rectifier and a smoothing capacitor. In this case, the half-bridge oscillator generates a high-frequency AC voltage supply for the flicker-free and low-noise operation of the discharge lamp.
A substantial disadvantage of discharge lamps as against incandescent lamps and halogen incandescent lamps has hitherto consisted in that it has not been possible to implement a dimming function in the case of operating units of discharge lamps. At this juncture, a proposal belonging to the prior art has provided an improvement in which interruptions in the power supply of an operating circuit for a discharge lamp are evaluated and serve to some extent as a trigger signal in order to cause the operating circuit when restarting to operate further in another operating state with a larger or smaller lamp current. It is possible thereby to distinguish and switch two operating states which permit the lamp power to be reduced in a way similar to a dimming function if required. For this prior art, reference is made to EP 0 488 002 B1 and the associated priority application DE 40 37 948.